Device for switching contact circuits for signaling purposes



Nov. 4, 1952 Z. VAN GELDER DEVICE FOR SWITCHING CONTACT CIRCUITS FOR SIGNALING-PURPOSES 2 snmtrs smam 1 Filed May 9, 1951 INVENTOR AGENT Nov. 4, l 952 z. VAl l GELDER DEVICE FOR SWITCHING CONTACT CIRCUITS FOR SIGNALING PURPOSES 2 SHEETS SHEET 2 Filed May 9, 1951 y I a d m,

[6Q Iii INVENTOR ZEGER VAN GELDER AGENT Patented Nov. 4, 1952 DEVICE FOR SWITCHING CONTACT CIR- CUITS FOR SIGNALING PURPOSES Zeger van Gelder, Eindhoven, Netherlands, as:-

signor to Hartford National ank a hat Company, Hartford, Conn., as trustee Application May 9, 1951, Serial No. 225;;43 In the Netherlands June 7, 1950 4; Claims. (Cl. 3159) The invention relates to devices of the kind comprising a tube suitable for efiecting electronic switching, said tube being adapted to perform the function of a plurality of relays.

In order that the invention may be more clearly understood and readily carried into eitect, it will now be described more fully with reference to the accompanying drawing, in which:

Figs. 1 and in. show characteristic currentvoltage curves of tube electrodes having suitable secondary emission characteristics;

Fig. 2 shows a device with reference to which the idea of the invention will be explained;

Figs. 3 and 3;]. show equivalent diagrams of the said device;

Fig. 4 shows diagrammatically a device according to the invention; and

Fig. 5 shows the equivalent diagram of this device.

Referring now to the drawing, and more particularly to Fig. 1, the uninterrupted curve shows the current of a secondary emitting auxiliary cathode HK if the collector electrode for the secondary electrons is kept at 200 volts. The dashed curve shows this current if the collector electrode is kept at 250 volts. If the auxiliary cathode is connected over a resistance R to a source of 70 volts (point P) the potential difference over the resistance is indicated by the full line B. The Voltage S, corresponding with the intersection of line B and the uninterrupted curve, is the voltage to which the auxiliary cathode rises if connected over resistance R to the source of 70 volts.

The collecting electrode 4 (Fig. 2), which has the form of a grid, can however also exhibit secondary emission and thus acts to some extent as an auxiliary cathode relative to electrode 5. The current of electrode 4 is indicated in Fig. 1a. As this electrode is not especially prepared to have a high secondary emission, it only produces a volta e U (about 100 v.) if connected over resistance R to a source of '70 volts. The significance of this will be explained hereinafter.

It has been suggested to make or break con tacts electronically. In such case, an electron beam was directed on at least one electrode having a secondary emission factor 6 1, said element co-operating with one or more further electrodes. The contact established between these electrodes by the electron ray made possible transmission'of alternating current signals.

However, it is not readily possible to connect a plurality of such contacts in series, as so often required. This applies particularly to telephone exchanges, in which a'plurality. of contacts in series establish a definiteconnectionor provide for the transmission'of definite signals. The latter circuits do not conveyff'speech currents, but only definite pulses, such as are required for busy signals, call signals, thema'intenance of speech connections or the interruption'thereof, and the like. "Since the electrodes between which the contact is established conduct current, subsequent serially connected contacts constitute a load for the preceding contacts, so that loss of voltage occurs. Furthermore, since the external resistances of various electrodes are connected in parallel, the resistance ultimately drops below'a permissible minimum value so that the tube becomes operative in the range 0Q of the current-voltage characteristic curve line R1 shown in Fig. 1, sothatl the signals to be transmitted are strongly. attenuated or distorted.

This disadvanta e could be obviated by introducing grid control as is shown in Fig. 2, thus causing operation as follows. The electron beam in from the electron gun I may be directed by means of deflection plates 2 and 6 on a system A1 or B1, in thisca'se on system A1. A plurality of secondary electrons exceeding the plurality of primary electrons and having a low velocity, are set free from an auxiliary'cathode 3, which is connected through a resistor R to a comparatively low voltage of, 'for example, .70 v. It is therefore necessary to provide a weak positive field before this auxiliary cathode in order to draw away the secondary electrons. Because of this flow of secondary electrons, the auxiliary cathode potential increases, 1. e. approximately to the voltage of the grid-shaped electrode 4. Since the electrode 4 is formed in the shape of a grid, the current flowing to this electrode will be very small, so that the auxilary cathode of the preceding tube is practically not loaded. Consequently, the resistance line R (Fig. 1 will ow on a sli h t r when a bsequ system is connected after this tube. The auxiliary cathode potential follows the voltage of the grid i (Fig. 2), so that alternating voltages and pulses supplied to the electrode 4 are transmitted to the auxiliary cathode 3 and from there, for example, to the corresponding grid-shaped electrode of the system A: of the next following tube. Alternating voltages supplied to the grid 4 can be transmitted in this manner through a definite series of contacts. If the beam Ill is directed on the system B1, signals from 8 can be transmitted. via 1 to a subsequent tube. The collecting-electrodes 5 and 9 have applied to'them a fixed positive voltage of, for example 200 v., whereas the deflection plate 2 can be held at a fixed voltage of 130 v. The switching operation by means of beam displacements is performed by voltage variations at 6 of, for example, from 70 to 200 v.

If pulses for signalling purposes and the like are supplied instead of speech currents, the voltage of an auxiliary cathode 3 may, as an alternative, be directly supplied to the deflection late 6 of a further tube, so that upon closing a contact A of a definite series of contacts, contact A2 or B2 of another series can be closed or interrupted. Such a tube replaces a relay having a change-over contact and, in addition two make and break relays, as shown in Fig. 3, or a relay having a make and break contact, as shown in Fig. 3a.

However, such an arrangement has the following disadvantages:

1. Since the resistance between the electrodes 3 and 4 has a finite value the voltage of the electrode 3 will not exactly increase to the value of 4, but remain slightly lower, 1. e. by a value of ST (Fig. 1). Consequently, each subsequent grid in a series of contacts will have a lower voltage than the preceding grid, so that the number of contacts to be connected in series is restricted.

2. The grids 4 and 8, which are also struck by the beam, will also have secondary emission, so that with respect to the collecting electrodes 5 and 9, they exhibit the same property as the auxiliary cathodes 3 and I with respect to the grids 4 and 8. Since the primary beam current at the grids is low relative to the beam current to the auxiliary cathodes 3 and I, the secondary emission current of these grids will not be sufficient to materially raise the potential of these grids, but the addition of these voltage-increases in a long series of contacts may nevertheless lead to excessive divergencies. Thus, the grids 4 and 8 will each increase in potential, for example, to a point U, indicated in Fig. 1a.

3. The electrodes interact upon each other, particularly if the beam moves from the system A1 to B1 when the grid 8 has a high potential and the grid 4 a low potential and, furthermore, when two pairs of systems which are both controlled by one beam are superposed.

The said disadvantages may be obviated by using a device comprising an electron tube accorde ing to the invention the tube providing, moreover, definite advantages.

In a device for effecting electronic switching, this tube comprises at least one electron gun and at least one pair of deflection plates, which are capable of directing an electron beam to different electrode systems. These systems are housed pairwise in the tube and each comprises at least one auxiliary cathode, the surface of which is satisfactorily secondary emissive, and at least one grid, and a collecting electrode for the secondary electrons, which is a screen plate connected to a fixed high positive voltage and provided between the systems of each pair, this plate constituting the common collecting electrode for these two systems. Provision is made in each system of a plate-shaped first control electrode, located opposite to this screen plate, Provision is further made of a plate-shaped second control electrode held at zero potential or at a low potential in each electrode system located approximately in the plane of the first control electrode between this electrode and the deflection plates.

Such a device is shown in A and c mprises a tube having one pair of systems. However, it is advantageous to house a plurality of pairs of systems, for example, four, in one tube. In this case the pairs may be arranged pairwise over one another on either side of the primary cathode, the electrons being concentrated in two ribbon-shaped beams, each at the level of two superposed systems. The cathode is of normal size and the tube itself has no abnormal dimensions. The beam emanating from the electron gun II is directed by the deflection plates I2 and I9 to the systems A or B. Each system has again one auxiliary cathode I 3 and 20, a grid I4 and 2 I, arranged before the auxiliary cathode and a first control electrodes I5 and 22. This electrode is capable of directing the beam to the associated auxiliary cathode or to the common collecting plate I'I, when the beam is directed by the defiection plates I2 and I9 to the system A or B. The collecting plate I! is directly connected to a screen-grid I8. The screen grid serves to make the strong positive field near the edge I'Ia of the collecting plate more uniform. This positive field is produced in that the electrodes I2 and IS, IS and 23, I5 and 22, which are near this edge, may have a low potential. The screen grid I8 prevents this positive field from deflecting the beam to the collecting plate, when the beam moves from the system A to the system B. Provision is further made of second control electrodes I6 and 23, which are held at low potential and the operation of which. will be set out more fully hereinafter. v

The operation of the tube in this circuit is described below.

By means of the potential of the deflection plate I9 the beam is directed to the system A or B. The deflection plate I2 has a fixed potential of, for example, v. If the potential of plate I9 is made lower than that of plate I2 by applying a voltage from +50 v. to +70 v. to plate I9, the beam moves to the system A; if the potential of plate I9 is raised from to 200 v., the beam moves to the system B. Therefore, the plate I9 determines the choice of the contacts A or B.

It is assumed that the beam is at the system A, and that the first control electrode I5 has the same potential as the auxiliary cathode I3, i. e. about 70 v., or a lower potential. The beam is then deflected towards the collecting plate IT as indicated by the full line in system A and does not impinge on the auxiliary cathode I3. The voltage at I5 is not critical but can differ to some extent without influencing the working of the tube. If this voltage is somewhat raised, the beam travels along the dashed line; if the potential on I5 is somewhat lowered, the beam will travel along the dash and dot line.

Only if the potential at I5 is raised considerably, e. g. to about 200 v., the beam will switch over from electrode I! to the auxiliary cathode, as indicated for system B (full line) In this case the voltage at plate 22 can be somewhat lower or higher than 200 volts, in which case the beam will travel along the dashed or the dash and dot line, respectively.

If the beam is directed on the auxiliary cath ode I3 or 20, the potential of this cathode ad justs itself to approximately the same value as that of the grid I4 or 2|.

Two possibilities are given here:

1. When the grid I4 is directly connected to the collection plate H, the electrodes I5 and I3 constitute the contact of the relay. The auxiliary cathode I3 may thus have two defined volt ages i. e. '70 v. or the v ,ltage. of the grid electrode M, which is connected. to the fixed battery voltage of 200 v. Consequently, this circuit. can only be used for the transmission of pulses.

2. When the grid I4 is a separate unit, the combination of the electrode It with the auxiliary cathode l3 will, moreover, provide the same eflect as the device shown in Fig. 2.

An alternating voltage across the first control electrode 15 or 2-2 is transmitted to the auxiliary cathode l3 or 20, respectively, as a step voltage. The leading and trailing edges of the step voltage may be made very steep by providing the auxiliary cathodes with slanting edges 24 and 25, so that the end of the beam, upon leaving or striking the auxiliary cathode, experiences an additional deflection owing to these edges, so that the beam takes up here an unstable position and a response characteristic curve is obtained.

The second control electrodes l6 and 23 have the effect that, if the beam were excessively de flected by the deflection plates I2 and I9 and if it tended to go off the outer side of the auxiliary cathode, the beam is bent, since it then brushes past the electrodes I6 and 23, which are held at a low potential (+or relative to the cathode, preferably at zero potential. The course of the beam is, in this case, as indicated in the systems A and B for an open and a closed contact, respectively. The broken lines indicate the course at a slightly stronger deflection, the dot and dash line at such a strong deflection of the beam that the deflection plates are strongly operative. This results in that a great variation of the deflection voltage across the deflection plates l2 and I9 is possible, while comparatively narrow auxiliary cathodes may be used, since, at a constantly increasing deflection voltage, the beam strikes the auxiliary cathode on the side of the collecting plate and leaves the auxiliary cathode also on the same side and is therefore capable of covering the width of the auxiliary cathode two times, without the operation being affected. It is thus possible to keep the entire system narrow, in contradistinction to the embodiment shown in Fig. 2.

A tube as shown in Fig. 4 replaces a combination of five relays, of which one relay has one change-over contact (deflection plates [2 and I9) and four unipolar make and break relays, as shown in Fig. 5, if the grids l4 and 2| are constructed as separate units. By suppressing the beam with the use of a control electrode, the function of a make-and break relay may be added to the combination. It is obvious that for each pair of systems, which is, moreover, housed in the tube and is struck by the same beam, a combinationpf four additional relays may be replaced. A preferred construction is obtained, when on either side of the cathode in the tube are each time arranged two pairs of systems, the cathode supplying two ribbonshaped beams.

Such a tube occupies materially less space than a corresponding number of relays.

The advantage of the construction according to the invention relative to other constructions, as shown in Fig. 2, is that the first control electrodes I5 and 22 are not located in the course of the beam and hence do not conduct current and, consequently, do not cause a voltage variation or loading of the electrodes of preceding tubes connected to them.

The circuit shown in Fig. 4 has proved to be very useful for signalling purposes in telephone exchanges; since many contacts can be connected in series without, causing a harmful voltage drop, since the voltage of each auxiliary cathode I3, 20. adjusts itself, irrespective of the preceding; control voltages, to the fixed voltage of the grids [4V and 2| connected to the collecting Plate, l1, whereas the deflection plates l8, l9, l5 or 22 connected to the auxiliary cathodes l3 and 20 of subsequent tubes do not conduct current. The use. of equal voltages for auxiliary cathodes and first control electrodes has the advantage that these parts can be directly interconnected, while moreover, there is no need of using energy-absorbing potentiometers.

What I claim is:

1. Electronic switching apparatus formed by a plurality of switching elements, each element being constituted by a cathode ray device comprising an electron beam source, a pair of electrode systems, a collecting plate electrode separating said systems, and deflecting elements for directing said beam into either of said electrode systems, each system being provided with an auxiliary cathode which emits secondary electrons when impinged upon by said beam, a grid inserted in front of said auxiliary cathode in the path of said beam, a first control electrode disposed without said beam path and a second control electrode disposed without said beam path between said first control electrode and said deflecting elements, means to maintain said second control electrode at a low potential, means to apply a potential to said collecting plate at which in the condition wherein the voltage applied to the first control electrode falls below a predetermined value said beam is collected by said collecting plate electrode, means to apply relative potentials to said auxiliary cathode and said grid at which in the condition wherein the beam strikes the auxiliary cathode said auxiliary cathode and said grid attain a condition of equi-potential, and means to intercouple said switching elements to effect a desired switching function.

2. Electronic switching apparatus formed by a plurality of switching elements, each element being constituted by a cathode ray device comprising an electron beam source, a pair of electrode systems, a collecting plate electrode separating said systems, and deflecting elements for directing said beam into either of said electrode systems, each system being provided with an auxiliary cathode which emits secondary electrons when impinged upon by said beam, a grid inserted in front of said auxiliary cathode in the path of said beam, a plate-shaped first control electrode disposed without said beam path, a plateshaped second control electrode disposed without said beam path between said first control electrode and said deflecting elements and a screen grid, means to maintain said second control electrode at a low potential, means to maintain said screen grid at a high potential, means to apply a potential to said collecting plate at which in the condition wherein the voltage applied to the first control electrode falls below a predetermined value said beam is collected by said collecting plate electrode, means to apply relative potentials to said auxiliary cathode and said grid at which in the condition wherein the beam strikes the auxiliary cathode said auxiliary cathode and said grid attain a condition of equipotential, and means to intercouple said switching elements to effect a desired switching function.

3. Apparatus as set forth in claim 2 wherein said screen grid and said collecting plate electrode are directly connected. 7

4. Apparatus as set forth in claim 2 wherein the edge of the auxiliary cathode adjacent to the collecting plate electrode is bent.

ZEGER VAN GEIDER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Skellett July 11, 1939 Gray Sept. 10, 1940 Hansell June 24, 1941 Preisach et a1. Dec. 9, 1941 Harries June 30, 1942 Nagy et a1. Nov. 10, 1942 Selgin June 7, 1949 Rosen July 26, 1949 Anderson Apr. 3, 1951 Jonker et al. Apr, 3, 1951 Adler May 22, 1951 

